Expression of SAMHD1 and its mutation on prognosis of colon cancer.

The expression of sterile α motif and histidine/aspartic acid domain-containing protein 1 (SAMHD1) and its mutation play a key role in the prognosis of colon cancer. The aim of the present study was to investigate the mechanism and the role of SAMHD1 in colon cancer. Microarray data from 187 patients with colon cancer and 45 adjacent normal tissue obtained from the Gene Expression Omnibus (GEO) were analyzed. A protein-protein interaction (PPI) network was constructed to identify key genes associated with colon cancer prognosis. Cox proportional hazard regression and survival analyses were performed to identify the potential for SAMHD1 to serve as a prognostic biomarker. Immunohistochemistry (IHC) and immunofluorescence (IF) were performed to assess the expression levels and distribution of SAMHD1 in tissues and cells. Western blotting (WB) and Cell Counting Kit-8 (CCK-8) assays were used to identify the proliferation and apoptotic effects of SAMHD1 on HT-29 (Cas9-SAMHD1) cell lines. A total of 6,905 consistently differentially expressed genes were identified in the GEO database. Through the PPI network, SAMHD1 was found to be associated with Kirsten rat sarcoma virus (KRAS). SAMHD1 expression was negatively associated with KRAS. Proportional hazards regression and survival analyses demonstrated that low expression of SAMHD1 was associated with increased patient mortality. IHC and IF results demonstrated that SAMHD1 expression in patients with colon cancer was decreased compared with controls (both P<0.05). CCK-8 and WB results showed that proliferation was significantly promoted, and the expression levels of apoptosis-related proteins were significantly inhibited in the D137N and D311A groups as a result of a mutation in the deoxynucleoside triphosphohydrolase (dNTPase) site (both P<0.05 vs. wild-type). Proliferation was inhibited and apoptosis-related protein expression levels were promoted in the wild-type (WT) and D137N groups following 20 µg/ml 5-fluorouracil (5-FU) treatment (both P<0.05). WB and CCK-8 results showed cell proliferation was promoted and cell apoptosis-related protein expression was inhibited in the D137N group following treatment with 20 µg/ml 5-FU (all P<0.05) compared with the WT group. In conclusion, SAMHD1 expression was low in colon cancer. The dNTPase function of SAMHD1 may inhibit colon cancer cell proliferation and may enhance apoptosis. In addition, first-line chemotherapy with 5-FU has a time-dependent effect, which may provide novel options for clinical treatment of colon cancer.